Various map services employ vector data to represent geographical features such as roads, rivers, lakes, countries, continents, oceans, etc. For example, a geographical feature or object may be represented by connecting the vertices of one or more vectors. While the great majority of these features are relatively small, for example, about 1-1.5 kilobyte, a significant number of them may be extremely large, for example, on the order of a megabyte or larger. The largest features may involve hundreds of thousands, or sometimes millions of vertices. Transmitting all of this information to a client device to render these features at all zoom levels based on their original geometry is impractical and wasteful of computing resources.
These map services may receive a request from a client device for a map of a given location and, in response, transmit a portion of the map information for display on the client device. These services may also transmit highly accurate map information as vector data and allow the client device to render the map at various zoom levels based on the same information. In other words, the client device may not request a new map each time the user “zooms” in or out of the map. Rather, each “zoom” level is redrawn based on the vector data received from the service.
Thus, the same amount of data and accuracy exists when the client device renders the map at the highest zoom level as at the lowest zoom level. However, at the lowest zoom level many objects may no longer be visible as they may overlap one another or be drawn within a single pixel. For example, as a user zooms out, such that a larger geographic area is displayed, many of the details of an object may be obscured as more of the map information is packed into a smaller area and less and less of the object's vertices are distinguishable.
For example, a user may examine the coast of Massachusetts in order to explore the vector data representation of the Atlantic Ocean. The map information associated with the Atlantic Ocean may include well over a million vertices. However, when zooming out at world level, all of the finer details in the geometry of the Atlantic Ocean (or the Massachusetts coastline) are no longer distinguishable. Many of the vertices that make up the Atlantic Ocean may actually overlap on the same screen pixel. Thus, rendering the Atlantic Ocean at such a high zoom level does not require the same level of accuracy as when exploring the coastline of a particular Massachusetts town.